The present invention relates to an improvement in spikes for sport shoes, and more particularly, to an improved spike design that allows a runner to stabilize kicks and to develop maximum propulsion during running without damaging a track.
During running in track and field sports, the load on the runner""s sole transfers in correspondence with the running movement of the runner. That is, an outer peripheral rear portion of the heel first contacts the ground surface and then the outer peripheral side of the foot arch, the projection of the fifth toe (little toe) and the projection of the first toe (big toe) sequentially contact the ground surface and finally the first to fifth toes contact and kick the ground surface. During the kicking movement, the pressing force of the toe portion of the shoe sole against the ground surface and the repulsive force from the ground surface develop propulsion in order to propel the runner in the forward direction.
During running, in order to enable the runner to exert the most forward propulsion obtained by the kick, it is necessary to prevent the spike disposed within the toe portion of the sport shoes from slipping backward and further to minimize the frictional resistance generated when the spike that pierces the ground surface is pulled out so that the spike can be smoothly pulled out. In other words, it is necessary to strengthen the ground gripping force of the spike and to develop maximum forward repulsion from the ground surface.
FIG. 11 shows seven pin-shaped spikes 95 secured to a front portion 93 of a shoe sole 92 of a shoe 91 of a pair of sport shoes. Designated by numeral 94 is a rear portion of the shoe sole 92.
Further, Japanese Utility Model Publication No. 48-30448 discloses a pin-shaped spike of shoes for track and field sports, which spike includes a semicircular groove formed in the left and right side surfaces of the spike and extends from a base portion to a tip end of the spike along the longitudinal central axis of the spike.
This pin-shaped spike easily pierces the ground during running. Further, by providing the grooves in the right and left side surfaces, the contact area with the ground is increased, and accordingly, the ground gripping force of the right and left side surfaces of the spike is increased. However, when kicking, the ground gripping force of the rear side portion of this pin-shaped spike is insufficient for stable kicks.
Further, in order to obtain stable kicks with this type of pin-shaped spike, the length of the spike must be 9 mm or longer.
However, with such a relatively long spike, the frictional resistance with the ground is increased when the spike, which pierces the ground surface, is pulled out during the kicking movement. Accordingly, the repulsion from the ground surface is significantly reduced and thus forward propulsion is reduced. In addition, if used on an all-weather type paved track, such a spike will damage the paved materials of the track.
It is, accordingly, an object of the present invention to provide a spike which does not have the above-described problems of the prior art and which can stabilize kicks during running movement so as to develop greater propulsion without damaging the track paving materials, and a sport shoe having such spike.
The present invention provides a spike, which includes a base, a claw formed on a tip end of the base and having a trapezoidal tip end portion, and a recess formed in a rear side of the base and extending from the claw to the base, the recess being curved relative to a longitudinal direction of the spike. With this construction, kicks during running movement can be stabilized, and damage to the track can be prevented.
Further, a collar is formed on an upper end of the base, and indentations are formed in the outer peripheral surface of the collar. A spike fixture includes a cylindrical portion having indentations, which indentations are formed on the inner surface of the cylindrical portion and engage the indentations of the collar. The spike fixture is secured to a shoe sole, and the orientation of the recess can be changed by changing the position of the engagement of the indentations. With this construction, maximum propulsion during running can be exerted by changing the orientation of the recess of the spike to correspond to the direction of the particular runner""s kick.